Technical Field
The present disclosure relates to a graphene-nanoparticle composite having a structure in which nanoparticles are crystallized at a high density in a carbon-based material, for example, graphene, and, more particularly, to a graphene-nanoparticle composite capable of remarkably improving physical properties such as contact characteristics between basal planes of graphene and conductivity, wherein nanoparticles are included as a large amount of 30% by weight or more, based on the total amount of the composite, and crystallized nanoparticles have an average particle diameter of 200 nm or more, and a method of preparing the same.
Background Art
In recent years, interest in nanotechnology has been increasing with the rapid development of electronics, info-communication and biotechnology, and nanopowder has been increasingly expected to be applied to various applications such as high-strength machinery parts, catalytics, medicine and biotechnology, as well as electrics and electronics, since nanopowder exhibits new peculiar physical properties which have not been exhibited by conventional powder, as the conventional powder is ground into highly fine particles.
Graphene represents a carbon structure with a 2D nanosheet single layer in which sp2 carbon atoms are used to form a hexagonal honeycomb lattice. Since the year 2004, when a group of Geim researchers in England separated graphene from graphite using a mechanical peel-off method, various reports regarding graphene have continued to be issued. Graphene is a compound which has come into the spotlight as an epoch-making new material due to the very high specific surface area (a theoretical value of 2,600 m2/g) compared with the volume, excellent electric conductivity (a reference value of 8×105 S/cm in an aspect of quantum mechanics), and physical and chemical stability.
In particular, graphene may function as a template on which a nano-sized transition metal oxide can be deposited due to a high specific surface area, excellent electric conductivity and physicochemical stability, and thus has unlimited applicability to energy storage materials for various devices (lithium ion secondary batteries, hydrogen storage fuel cells, and supercapacitors), gas sensors, micro-parts for biomedical engineering, highly functional complexes, and the like upon formation of nanocomplexes with transition metals.
However, graphene is not easily peeled off in a solution due to the presence of van der Waals interaction between basal planes of graphene caused by a sp2 carbon bond formed on a surface of the graphene, and is present in the form of thick multilayer graphene other than single-layer graphene. Also, graphene has a restacking property to be restacked even when graphene is peeled off. Therefore, graphene has problems in that it is impossible to make use of a high specific surface area of the single-layer graphene, and it is difficult to form a uniform composite structure. This serves as a factor inhibiting its use.
Also, graphene has characteristics such as high thermal and electric conductivity in a horizontal direction and low thermal and electric conductivity in a vertical direction between graphene layers, as viewed from a planar structure of graphene. Therefore, when graphene is applied to applied thermal or electric devices, an increase in thermal or electric contact resistance is caused according to a physical contact shape of a connection point between graphene and graphene, thereby inhibiting use of its innate high characteristics.
Accordingly, to solve the problem regarding the contact resistance between graphene and graphene, there is an increasing attempt conducted to enhance contact resistance by chemically depositing or attaching a nano-sized metallic material on/to a surface of graphene.
However, only the edge and defective parts of graphene are generally deposited when nanoparticles attempt to be deposited on graphene. In particular, there has been an attempt conducted to deposit nanoparticles on a surface of graphene using a wet process known in the related art. This wet process does not have an excellent effect of improving mechanical and electric characteristics of graphene since the nanoparticles are deposited on less than 10% of the surface of graphene. Sundaram et al. reported that palladium (Pd) nanoparticles are electrodeposited onto graphene, but that palladium (Pd) nanoparticles are deposited onto only the edge of graphene (Adv. Mater. 2008, 20, 3050). Also, a chemical wet process method is used to forcibly form a defective part, but has problems in that it is difficult to optionally form a defective part at a certain position or several positions, and the original structure, that is, a hexagonal honeycomb lattice with a single bond, of graphene may be damaged when defects are formed at too many positions, thereby inhibiting electrochemical or thermal characteristics.
Thus, there is an urgent demand for the development of a composite in which a large amount of a nanomaterial is deposited so as to improve reactivity in a basal plane of graphene, and a method of preparing the same.
Accordingly, the present inventors have found that a graphene-nanoparticle composite, in which nanoparticles crystallized in a surface of graphene are included at a high density, especially, the nanoparticles are included at a content of 30% by weight or more, based on the total weight of the composite, and the crystallized nanoparticles have an average particle diameter of 200 nm or more, can be obtained by fusing a nanomaterial with graphene using a radio-frequency thermal plasma process other than a conventional wet process. Therefore, the present invention is completed based on these facts.